1. Field of the Invention
The invention concerns a hydraulic elevator having a hydraulic drive with a pump connected for controlling the hydraulic drive and a method of controlling and automatically regulating the hydraulic elevator.
2. Description of the Prior Art
DE 40 34 666 A1 and corresponding U.S. Pat. Nos. 5,419,411 and 5,349,142 disclose a hydraulic elevator in which oil is conveyed by a pump between the hydraulic drive for the elevator car and the pressure accumulator, which is called a counterbalance elevator drive in the cited document. Each of the lines from the pump to the drive and from the pump to the pressure accumulator contains a speed control valve, with which the operating curve can be controlled. It is also disclosed that the pump is driven by an electric motor, which is controlled by an inverter.
In EP 829 445 A1, a device is shown, in which, under certain conditions, the motor coupled with the pump acts as a generator, so that excess hydraulic energy is converted to electric energy and can thus be recovered.
U.S. Pat. No. 5,281,774 A describes a control device for a hydraulic elevator, in which the electric motor that drives the pump is controlled by an inverter.
A hydraulic elevator with a pressure accumulator is also known from U.S. Pat. No. 5,579,868 A. In one of the embodiments of this elevator, a first pump is connected between the hydraulic drive for the elevator and the pressure accumulator and is used to control the flow of hydraulic oil between the hydraulic drive and the pressure accumulator. The first pump is coupled with a hydraulic motor, by which a controllable split stream of the hydraulic oil flows to the tank, such that energy is produced from the pressure difference during the depressurization of the hydraulic oil from the hydraulic drive or pressure accumulator to the unpressurized tank, and this energy is used in the operation of the first pump. Hydraulic oil can be conveyed from the tank to the pressure accumulator to refill the pressure accumulator over and over again.
In WO 98/34,868 and corresponding U.S. Pat. No. 6,142,259, the pump for conveying hydraulic oil in a hydraulic elevator is operated by an electronic power regulating unit. Power regulating units of this type are also known as variable-frequency inverters.
Another device for operating a hydraulic elevator is known from WO 99/33740 and corresponding U.S. Pat. No. 6,347,515. In this case, a pump and four line branches, each with an electrically actuated valve, are installed between the hydraulic drive and the pressure accumulator. When the elevator is moving up, two of the valves must be opened, and when it is moving down, the other two valves must be opened. The pressure accumulator apparently has three pressure spaces, which is more clearly evident from the application FR 2 773 141 A, on which the priority of WO 99/33740 is based. How the speed is controlled remains unclear. It may be assumed that large pressure surges occur when the four electrically controllable valves are actuated.